Abstract
In the energy distribution grid of electric vehicles (EVs), multiple different voltage potentials need to be interconnected, to allow arbitrary power flow between the various energy sources and the different electrical loads. However, between the different potentials, galvanic isolation is absolutely necessary, either due to safety reasons and/or due to different grounding schemes. This paper presents an isolated three-port DC/DC converter topology, which, in combination with an upstream PFC rectifier, can be used as combined EV charger for interconnecting the single-phase AC mains, the high-voltage (HV) battery and the low-voltage (LV) bus in EVs. The proposed topology comprises two synergetically controlled and magnetically coupled converter parts, namely, a series-resonant converter between the PFC-sided DC-link capacitor and the HV battery, as well as a phase-shifted full-bridge circuit equivalent in the LV port, and is mainly characterized by simplicity in terms of control and circuit complexity. For this converter, a simple soft switching modulation scheme is proposed and comprehensively analyzed, in consideration of all parasitic components of a real converter implementation. Based on this analysis, the design of a 3.6 kW, 500 V/500 V/15 V prototype is discussed, striving for the highest possible power density and as low as possible manufacturing costs, by using PCB-integrated windings for all magnetic components. The hardware demonstrator achieves a measured full-load efficiency in charge mode of 96.5% for nominal operating conditions and a power density of 16.4 kWL−1.
Highlights
Electric vehicles (EVs) are increasingly gaining market share in the automotive sector, partly because of the ever shorter charging times, which can currently almost compete with the refueling times of conventional vehicles with combustion engines
It is possible to get a good impression of the performance of the system presented by comparing the efficiency and power density with an isolated two-port DC/DC converter with similar specifications [13] (PCB-integrated magnetics, 3 kW, Vin = 400 V, Vout = 12 V), which could be used in EV applications as supply for the LV-bus
Even though the proposed topology is perfectly suitable for the application at hand, there is still room for improvement in terms of hardware implementation, as especially the partial-load efficiency in nominal charge mode (CM) operation is limited by the large circulating currents in the LV-port
Summary
Electric vehicles (EVs) are increasingly gaining market share in the automotive sector, partly because of the ever shorter charging times, which can currently almost compete with the refueling times of conventional vehicles with combustion engines. The component utilization can be improved by combining the OBC with another converter system usually installed in EVs, namely the galvanically isolated DC/DC step-down converter, which feeds energy from the HV-battery to the low-voltage (LV) bus [4] As this converter is mainly operated in drive mode and has a similar power rating of 3 kW, an integration of both systems into a single unit with a total power rating of 3.6 kW seems very promising. The overall topology should be as simple as possible both in terms of design optimization as well as control, in order to guarantee the suitability for industrial applications In this paper, such novel three-port converter topology for a combined EV charger is derived, which provides galvanic isolation between the HV-battery, the LV-bus and the DC-link capacitor of an upstream single-phase PFC rectifier, which, is out of the scope of this paper.
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